CharacteristicsHead looks large in proportion to its body; no ear tufts. Very tame, but small, nocturnal and easily overlooked. Migrates; has a very large increase in migrating numbers (an "irruption") about every 30 years. Nests in cavities in dead stubs, mostly old flicker nests. Call is a mellow whistled note repeated mechanically in endless succession. Common name is derived from call's resemblance to sound of a saw being sharpened.